The present invention relates to products and methods for maintaining or increasing the intracellular concentration of ceramides. More particularly, the present invention relates to the use of certain agents, such as botanical extracts, in wipes and absorbent products to maintain or increase intracellular ceramide concentrations. Intracellular ceramide concentrations are maintained or increased in the present invention by introducing one or more agents capable of increasing the activity of sphingomyelinase and/or decreasing the activity of ceramidase.
Ceramide (N-acylsphingosine) is a lipid metabolite and is an important intracellular messenger which is released inside a cell within a few hours of stimulation with various agents. Ceramide is regarded as a second messenger in the context of the sphingomyelin signal transduction pathway, and fulfills an important role in the moisturizing mechanism and barrier mechanism of skin. Ceramides are released by sphingomyelin as a result of the enzymatic effect of sphingomyelinases, which are forms of phospholipase C specific for sphingomyelin. Inside the cells, ceramide can influence growth and differentiation, regulate protein secretion, induce DNA fragmentation and apoptosis, and increase the synthesis and secretion of cytokines. Hydrolysis of sphingomyelin occurs rapidly after exposure of the cells to exogenous sphingomyelinase or to agonists which activate endogenous sphingomyelinases.
The importance of ceramides in the skin metabolism and health is well documented. The main cellular constituents of the epidermis are keratinocytes, melanocytes, Langerhans cells, fibroblasts, endothelial cells and macrophages. The intracellular space consists mainly of neutral lipids, glycoproteins, protein degradation products, desmosomes, active enzymes, products of sebaceous glands, and ceramides. As long as this brick and mortar structure is intact, the skin is endowed with both a protective layer and a selectively permeable filter.
During the differentiation process of the epidermis, which starts with cell division in the basal layer and ends with the death of keratinocytes and the development of the lipid barrier, the cells modify their lipid synthesis capability. The result is that the basal layer of the epidermis is characterized by phospholipids and cholesterol, whereas the outermost layer is characterized by cholesterol, free fatty acids and ceramides. The lipids of the horny layer, the main component of which consists of sphingolipids, play a crucial role in maintaining the permeability barrier of the epidermis to water. The sphingolipids are exuded from the lamellar bodies of the granular cells of the epidermis. Ceramides, which make up almost 50% of the horny layer of skin, are the main polar lipids of the horny layer and play a fundamental role in the barrier function of the skin against water leakage in cell adhesion and in the differentiation of the epidermis, as mentioned above.
Like the appearance of the surface of the skin, its functional properties also undergo changes with aging. Aging skin is characterized by a reduced water content in the horny layer associated with reduced transdermal leakage of water. It has been shown that ceramide concentration decreases with age, and this decrease may be responsible for the dehydration of the skin which is observed in the course of aging. In addition, abnormal ceramide levels (deficiencies) have been detected in atopic eczema, dermatosis and dermatitis, atopic dermatitis and psoriasis.
In addition to age, other external factors can reduce the amount of ceramides present in the skin and lead to skin irritation problems. For example, the enzyme ceramidase can degrade ceramides to sphingosine and free fatty acids upon contact with ceramides. Ceramidase is present in skin in certain layers where it performs a beneficial conversion function. However, when ceramidase is introduced onto skin from an external source such as bacteria (bacterial ceramidases) present in feces or nasal secretions, the ceramidase can degrade ceramides as mentioned above thereby reducing the intracellular concentration of ceramides and leading to dry, cracked skin.
In light of the foregoing, it is useful to maintain high levels of ceramides in the skin to maintain and promote healthy skin. As such, it would be advantageous to produce personal care products, such as wet wipes and absorbent care products, capable of maintaining or increasing the levels of ceramides in the skin. Because controlling the ceramide levels in the skin by the addition of natural ceramides is not practical due to the enormous expense of the purified lipid, there continues to be a need for economical products containing agents capable of maintaining or increasing the levels of ceramides in the skin.